The present invention relates to a multilayer wiring structure, and more particularly to a through-hole connection structure between an upper pattern of a multiplicity wirings and a lower pattern of a multiplicity of wirings which are formed on and beneath an intervening insulation film.
As a device using such a multilayer wiring structure, there has been proposed, for instance, an intimate contact type optical sensor array as shown in FIG. 1. In the figure, reference numeral 1 denotes an original to be transmitted, 2 a light source comprising, for instance, a light emitting diode, and 3 a contact fiber substrate which is arranged to oppose the transmission original 1 and which is provided with a plurality of optical fibers 4 embedded in the surface into which the incident light from the light source 2 enters after being reflected on the transmission original 1. Reference numeral 5 denotes a glass substrate arranged to oppose the contact fiber substrate 3 and carrying a photo-detector (to be described later) on the part opposing the output terminal of the optical fibers 4, and 6 conductor electrodes of Cr-Al alloy deposited on the glass substrate 5 and also acting as wiring leads. Reference numeral 7 denotes a conductive film of n-type semiconductor such as CdSe formed on the conductive electrode 6, 8 a photoelectric conversion film of p-type semiconductor such as Se-As-Te family material formed on the n-type semiconductor 7, and 9 transparent common electrodes of, for instance, In.sub.2 O.sub.3.
In the optical sensor array device of such a structure as mentioned above, the light, L, from the light source 2 is reflected on the reading surface of the transmission original 1, converted to a light signal L' to be guided through the bundle of optical fibers 4 embedded within the fiber substrate 3 to the photoelectric conversion film 8, and then converted again into an electric signal from the light signal L'. After the conversion, the electric signal activates scanning circuits 10 and 11 for matrix driving as shown in FIG. 2.
In the intimate contact optical sensor array device constructed as above, since the intimate contact line sensor does not need to enlarge or reduce the picture image of the transmission original 1 by means of the lens system, the resolution becomes proportionate to the widths of the conductive film 7 and the conductive electrode 6 on the photoelectric conversion film 8 or in other words to the density of the microarray. That is, as illustrated in FIG. 3, the resolution is determined by an allowable number of the conductive films 7 and the conductive electrodes 6 to be formed on the photoelectric conversion film 8 which converts the light signal L' into an electric signal. In other words, it is determined by the array pitch, P, for the conductive film 7 and the conductive electrode 6. For example, in order to obtain a resolution of 8 per 1 mm, it is required that P=1-8=125 .mu.m. Typically, the conductive electrodes 6 are prepared by photoetching process, and amount to 1,800 in number for reading an A4 size original. Furthermore, although the longitudinal length of the glass substrate 5 is about 240 mm, the space reserved for wiring on the glass substrate is quite limited because a driving circuit, an external output connection terminal etc. (not shown) are formed on the periphery of the glass substrate. It is, therefore, extremely difficult to form about 1,800 conductive electrodes, straight or bent, on the glass substrate 5.
In order to realize a matrix array with about 1,800 conductive electrodes 6 in the optical sensor array device of the above mentioned type, a multilayer wiring structure becomes necessary. For instance, if 1,728-bit picture elements are arrayed in a matrix of 32.times.54, 1,728 through-holes and 1,727.times.32=55,264 or 1,727.times.54=93,312 crossovers will be formed. Thus, it is necessary to form 1,728 fine through-holes by photo resist process, and to make insulation between the through-hole contacts and the crossovers, thus degrading yield rate and reliability.